The invention relates to an implantable heart pacemaker comprising a battery whose internal resistance depends on the charge condition of the battery, as well as comprising a stimulus pulse generator connected to the battery having an output capacitor which is respectively slowly charged and is subsequently rapidly discharged for generating a stimulation pulse.
Such modern, implantable heart pacemakers employ batteries with a constant electromotive force whose internal resistance increases the more greatly the battery is discharged. That leads to the fact that the amplitude of the stimulation pulses decreases with an increasing discharge of the battery, since the output capacitor must be charged with a current which becomes smaller and smaller and, thus, can no longer reach its full voltage in the time available for charging. When the amplitude of the stimulation pulses falls below the threshold value characteristic for the patient, the stimulation pulses become ineffective.
Attempts have already been undertaken to extend the operating life of such a heart pacemaker in that the width of the stimulation pulses is increased as the battery discharges (German OS No. 2,301,055). Since, however, the threshold can only be influenced to a very slight degree by the width of the stimulation pulses, only an insignificant prolongation of the useful life can be achieved in this manner. Beyond that, the disadvantage of an increased power consumption per pulse derives given this method as, thus, does an accelerated discharge of the battery.